The present invention relates to a numerical control machine tool, and more particularly to improvements in signal transmitting and receiving equipment which performs transmission and reception of signals regarding M, S and T functions between a numerical controller and a machine tool.
Equipping a numerical controller (hereinafter referred to as an NC apparatus) with M, S, and T functions so as to improve its performance as an NC machine tool has heretofore been known. The M function is one that performs ON-OFF control for starting and stopping the rotation of a spindle, turning ON and OFF of a coolant and so forth in accordance with commands stored on a command tape. The S and T functions are those for similarly controlling the number of revolutions of the spindle and controlling the tool selection in accordance with commands stored on the command tape. These functions are performed by sending out signals regarding the M, S and T functions as relay contact signals to the machine tool and controlling its heavy current circuits.
The M, S and T functions serve to effect principal control of the machine tool and the control operations have to be carried out accurately because an erroneous operation would produce serious trouble, such as a breakdown of the machine tool or damage to an expensive workpiece. However, since data transfer between the NC apparatus and the machine tool is usually effected by parallel transfer which does not involve parallel-serial conversion and is high in transfer rate, and since a number of transmission lines and relays corresponding in number thereto are used, there are some occasions when a faulty signal is sent out owing to breakage of the transmission line or a breakdown of the relay. In such a case, according to a conventional arrangement, the faulty signal may be applied as it is to a heavy current circuit on the side of the machine tool to cause an erroneous operation. That is to say, in a prior art NC machine tool, such as for instance the one shown in FIG. 1, a code sending circuit 10, by which numeric codes following address characters M, S and T indicating the kinds of functions are transmitted in parallel via transmission lines l.sub.1 to l.sub.n having connected thereto relay circuits (not shown), is provided for each function on the side of the NC apparatus. A code signal sent out from the code sending circuit is received and decoded following a strobe signal sb in a decoding circuit 11 provided on the side of the machine tool, and the decoded signal is applied to the heavy current circuit of the machine tool. Accordingly, even if a wrong code is transmitted and received due to, for example, breakage of a transmission line l.sub.1 to l.sub.n or breakdown of a relay, since no error detecting means is provided on the receiving side, the machine tool operates following the wrong code.